Metamaterials or artificial Negative Index Materials (NIM) are a new class of electromagnetic materials or structures that have generated great attention over the last ten years due to their unique and exotic electromagnetic properties. They are constructed with specially designed inclusions and architecture in order to exhibit a negative index of refraction, which is a property not found in any known naturally occurring material. These artificially configured composites have a potential to fill voids in the electromagnetic spectrum where conventional material cannot access a response, and enable the construction of novel devices such as microwave circuits and antenna components. The negative effective dielectric constant is a very important key for creating materials with a negative refractive index.
To achieve a negative dielectric constant, two main approaches have been employed in the art. One approach involves the use of a periodic structure whose frequency spectrum mimics the response of a high pass filter or a waveguiding structure—for example a hollow metallic waveguide loaded with periodic split ring resonators. Under this condition, electromagnetic waves are evanescent at low frequencies and this evanescence in the small frequency gap is described in terms of negative permittivity values below some specific frequency (i.e., the corner (or cutoff) frequency). The second approach involves the use of a composite comprising of metal inclusions in a dielectric matrix. It has been verified experimentally on a micrometer level that the effective dielectric constant of a composite containing conducting micro-fibers (diameter ˜25 μm) was negative at GHz frequencies. It has also been proposed that a composite that consists of short ferromagnetic wires embedded into a dielectric matrix, can exhibit a tunable effective negative dielectric constant under a DC magnetic field.
The first approach in the art involves assembling periodic geometrical structures made up of inductors and capacitors on a micrometer scale, which is extremely difficult and not readily applicable for producing commercial metamaterials with conventional materials. The second approach in the art of using metal inclusions is not desirable because of the difficulty in making a homogenous material without aggregation. The limitation of tunability of the resonance frequency is another big problem with the two approaches, since the resonance frequency can be tuned only by dimensional change of the components in these systems. Accordingly, new ways of manufacturing materials, and materials themselves, are being continuously sought.